Field of the Invention
The invention relates to an operational amplifier with symmetrical inputs and symmetrical outputs.
Such operational amplifiers are supplied with symmetrical input signals, that is input signals which agree in amount but have a different sign with respect to a reference value. The output signals present at the symmetrical outputs of such an operational amplifier should accordingly have the same amplitudes with opposite signs. That means that the total of both signals should always be equal to zero as much as possible, which is equivalent to maximum common mode rejection.
One such operational amplifier is known from German Utility Model G 92 07 812.5. The circuit configuration described therein is constructed for a supply voltage of 4.5 V minimum. However, modern circuit configurations, especially for use in automobiles, require a minimum supply voltage of 2.7 V. Since the known amplifier circuit is constructed for 4.5 V, it contains cascodes for high idling amplification, as well as low-impedance push-pull output buffer amplifiers. Those circuit elements are a hindrance to operation at 2.7 V, because the configuration adds up to as many as four diode threshold voltages.